Lens trimming machines



Jul 1, 1969 J. LEVILLAIN ET AL LENS TRIMMING MACHINES Filed June 14,1966 United States Patent Int. Cl. B24b 7/00, 9/00 U.S. Cl. 51-101 4Claims ABSTRACT OF THE DISCLOSURE Spectacle lens trimming machine havinga grinding wheel and a control follower against which are respectivelypressed 2. lens to be trimmed and a template of selected shape. Anelectrical circuit means is provided for reversing the direction ofrotation of the lens and templet upon contact of the follower with thetemplet.

Machines for automatically trimming lenses, notably spectacle lenses,are already known, wherein a lens carrier rotated at a relatively slowrate and a grinding wheel driven at a relatively high speed are urgedagainst each other, the penetration of the grinding wheel into the lenscontour being limited by a fixed follower solid with the wheel mountingand adapted to engaged a templet attached to the lens carrier.

In certain known machines of this type the lens carrier is rotatedcontinuously in the same direction. In this case the lens carrierperforms a number of revolutions subordinate to the necessarypenetration in front of that point of the final contour which is thedeepest one with respect to the initial contour. Thus, the grindingwheel passes again and again on finished circular arcs of the contour,thus retarding the trimming operation.

To avoid this inconvenience trimming machines have been devised whereinthe lens rotation is stopped until the templet contacts the roller. Thusthis rotation is resumed but it is stopped again when the excessthickness of the follower stops the templet-to-lens contact. Thisarrangement is advantageous in that it avoids a great number of passeson lens portions requiring a lesser penetration, thus affording aconsiderable gain of time. On the other hand, in the case ofparticularly flattened shapes, the penetration of the grinding wheelbeing relatively deep during the first period of the operation, thestress or torque applied for starting the movement of rotation of thelens is extremely high as the wheel has penetrated the lens material toa substantial depth. This stress produced between the lens and thegrinding wheel is frequently attended by a rupture or a rotationalshifting of the lens in relation to its templet.

It is a primary object of this invention to provide an automatictrimming machine operating at least as fast as known machines of thesecond type described hereinabove, but free of the abnormally severereactions and risks of breakage observed heretofore in machines of thistype.

To this end, the trimming machine according to the present inventioncomprises reversing means adapted to reverse the direction of rotationof the lens carrier as a function of the relative positions of thetemplet and fixed follower. Thus the machine operates by producing analternate and relatively fast rotation along each penetration section ina manner similar to a manual machine controlled necessarily by a veryskilled operator.

This invention further comprises means for prevent- 3,452,484 PatentedJuly 1, 1969 ing reversals of the direction of rotation of the lenscarried in case the excess thickness to be removed by the grinding wheelis too small to develop an excessive resistance to the continuation ofthe lens rotation in the same direction.

The features and advantages of this invention will appear morecompletely from the following description given by way of example withreference to the attached drawings in which:

FIGURE 1 is a diagrammatic view showing the lens to be cut and thegrinding wheel in an automatic machine of the second type mentionedhereinabove, during a step in which the fixed follower has engaged thetemplet.

FIGURE 2 shows, on the surface of the lens to be trimmed which ismounted on the machine according to this invention, the path followed bythe point of penetration of the grinding wheel into the lens until thetrimming of one side ofthe final contour is completed.

FIGURE 3 shows on the same lens the paths followed by the same point ofpenetration of the grinding wheel during the trimming of the next lensside.

FIGURE 4 is a schematic layout of the whole of a trimming machineaccording to the invention.

FIGURE 5 shows the paths followed by the point of penetration of thegrinding wheel into the lens, in a trimming machine completed by adevice for automatically limiting to a maximum angular amplitude therotation of the lens in one direction.

In the known machine of the second type described hereinabove, the lenscarrier remains stationary until the fixed follower carried by themounting of the grinding Wheel M contacts the templet H rigid with thelens carrier. At this time, as shown in FIGURE 1, the wheel becomestangent at A to the final contour to be given to the lens V, and anelectric contact provided between the roller and the templetre-energizes the means for rotating the lens carrier, whereby thegrinding wheel M grinds an arc AB through a relatively great thickness,so that the rotation of the lens carrier is counteracted by an abnormalresistance.

The inconvenience is removed in the trimming machine of this inventionwhich operates in the manner illustrated in FIGURE 2. In this machinethe contact between the follower and the templet H controls thereversing of the direction of rotation of the lens carrier and,therefore, of the lens V carried thereby. Under these conditions, thepath followed by the point of penetration of the grinding Wheel into thelens, from an initial point 0 on the initial lens contour, describes aseries of curvilinear arcs in alternate directions. From this second arcAB each arc starts from a point A of the final contour and leads toanother point B of the same contour. The length of these successive arcsAB, BC, CD decreases as well, of course, as the duration of their path.When this duration becomes very moderate, for example in the case of arcCD, it is no more advantageous to impress a rapid to-and-fro motion tothe lens, it being obviously more advantageous to continue the rotationin the same direction. This result is obtained as seen in FIG. 4 bycompleting the pilot electrical circuit controlling the reversing of thetemplet and lens carrier actuating motor with time-lag means permittingthe reversal of the direction of motion of the lens carrier only if thetime period elapsing between two successive contacts between thefollower and the templet exceeds a predetermined, properly selectedlower limit. With this arrangement the lens being trimmed continues torotate without reversing its direction of rotation when the contact isat D, and thus the wheel enters the zone E where reversals are resumed,the grinding wheel moving in succession to points E, F, G. Thus, thework is performed by successively reducing each one of the larger sidesof the lens without causing the grinding wheel to pass several times onthe previously ground sections. According to this invention, the machineis completed by an electrical device capable of stopping the machinewhen a complete uninterrupted rotation has taken place. The reversal maybe controlled by using mechanical means or preferably a reversibleelectric motor, as diagrammatically shown in FIG. 4, the reversingaction being simply exerted on the energizing conductors.

In a modified form of embodiment the recurrence of the changes in thedirection of travel of the grinding wheel is limited by a devicecontrolling these changes only when the excess thickness of the contourin relation to the desired final contour exceeds a predetermined,properly selected limit, In this arrangement shown in FIG- URE 4 theelectric contact between the templet H and the fixed follower T isreplaced by a contact between the follower T and an auxiliary feeler I.Then the follower T is stationary and carried for example by a resilientblade R mounted on the same structure I as said resilient feeler I. Astop K limits to a value a the permissible movement of follower Tagainst the elastic resistance of spring R. The distance b between thecontact feeler I and the inferior to a. Since the reversal is controlledby contact pulses, it cannot take place when the excess thicknesses ofthe lens during the grinding operation such as S, with respect to thefinished contour, are inferior to a-b.

With this device minor extra thicknesses cannot cause the reversal ofthe direction of movement of the grinding wheel, whereas this reversalis maintained in case of substantial extra thicknesses. Thus, as by theuse of the aforementioned time-lag means, an abnormally high rate ofrecurrence of these reversals, which took place heretofore at the end oftrimming operations, are safely avoided.

In the case of special contours wherein the first reversal might takeplace too late and to increase the machine output, control pulses may befed to the reversing means in order to alternate the direction ofrotation between the initial point and the first actual contact point A.Thus, successive artificial reversals A1, A2, A3, A4 are produced beforethis first contact A takes place. In this case the removal of glassparticles develops in the manner illustrated in FIGURE 5, thesereversals accelerating the initial grinding operation. Since thesereversals are controlled through electrical means such as timers orcapacitor charges they can be adjusted as a function of the type of workto be performed and notably to the abrasion resistance of the lensmaterial.

The slow lens rotation may be obtained by utilizing a reduction gearingof the type already known per se, or better a floating-rotor motor ofthe steromotor type capable of reversing its motion frequently withoutinertia What we claim is:

1. A machine for trimming lenses, particularly spectacle lenses,comprising a circular grinding wheel rotating rapidly about its axis afollower having a control surface of circular contour of the same radiusas the grinding wheel and coaxial with the grinding wheel, a templet ofselected shape fixed with respect to the lens to be trimmed and disposedin front of said follower while the lens to be trimmed is disposed infront of the grinding wheel, means for pressing said lens and saidtemplet toward said grinding wheel and follower and for imparting slowmovement of rotation as long as said templet does not contact saidfollower and electric circuit means for reversing the direction ofrotation of said lens and templet upon contact of said follower withsaid templet.

2. A machine for trimming lenses, particularly spectacle lenses,comprising a circular grinding wheel rotating rapidly about its axis, afollower having an operative portion with a circular contour of the sameradius as the grinding wheel, a first elastic and conductive bladecarrying said follower, abutment means for stopping said followercarried by said elastic blade in a position in which operative portionof the follower is concentric with said grinding wheel, a second elasticand conductive blade carrying a contact which is separated from saidfirst blade when no force acts on said follower and which engages saidfirst blade when a force acts on said follower to move said follower tosaid abutment means, a templet fixed relative to the lens to be trimmedand disposed in front of said follower while said lens is disposed infront of the grinding wheel, means for pressing said lens and templettoward said grinding wheel and follower, electric motor means for slowlyrotating said lens and templet, means for reversing the direction ofrotation of the motor, an electric control circuit for controlling thereversing of said motor, said circuit including said first and secondelastic blades and being closed to reverse said motor when said templetengages said follower to move the follower toward said abutment meansand thereby make contact between said first and second blades.

3. A lens trimming machine according to claim 2, comprising adjustabletime delay means in said electric circuit and permitting reversing ofsaid motor only when a closing of said circuit follows a precedingclosing by an interval of time greater than that for which said delaymeans 1s set.

4. A lens trimming machine according to claim 3, in which the contactbetween the two elastic blades is maintained when said follower isspaced from said abutment means by a slight amount.

References Cited UNITED STATES PATENTS 1,231,920 7/1917 Lumsden 51-101 X2,723,501 11/ 1955 Lueck. 2,821,050. 1/ 1958 McCarthy. 3,119,206 1/1964-Baumgartner. 3,210,890 10/ 1965 Lannom.

LESTER M. SWINGLE, Primary Examiner.

D. G. KELLY, Assistant Examiner.

